1. Field of the Invention
The present invention relates generally to flow measuring devices, and more particularly to flow measuring devices in which a plurality of channels are defined in a common rotating or oscillating conduit unit with flow through certain of the channels in a given direction being additive and flow in other of the channels in the opposite direction being subtractive. Also, enhanced flow measurement of a single stream of loose or aerated material is provided by flowing such streams through multiple flow channels rather than a single, larger flow channel. 2. Description of Related Art
Flow meters of the general type with which the present invention is concerned have been known as gyroscopic mass flow meters, or Coriolis force mass flow meters. In essence, the function of both types of flow meters is based upon the same principal. Viewed in a simplified manner, Coriolis forces involve the radial movement of mass from a first point on a rotating body to a second point. As a result of such movement, the peripheral velocity of the mass changes, i.e., the mass is accelerated. The acceleration of the mass generates a force in the plane of rotation and perpendicular to the instantaneous radial movement. Such forces are responsible for precession in gyroscopes.
A great number of approaches have been taken in utilizing Coriolis forces to measure mass flow. For instance, the Roth U.S. Pat. Nos. 2,865,201, 3,276,257, and 3,312,512 disclose gyroscopic flow meters employing a full loop which is continuously rotated (DC type), or oscillated (AC type).
Another flow meter utilizing substantially the same forces but avoiding reversal of flow by utilizing a less than 180.degree. "loop" is described in Sipin U.S. Pat. No. 3,485,098. The device is of the so called AC type, i.e., the conduit oscillates around an axis and fluid flowing through the conduit flows first away from the center of rotation and then towards the center of rotation thus generating Coriolis forces as a function of the fluid mass flow rate through the loop.
Since there is but one means of generating Coriolis forces, all of the prior devices of the gyroscopic and Coriolis force configurations generate the same force, but specify various means for measuring such forces. The instant invention is applicable to any Coriolis flow meter.
A device similar in appearance to the preferred embodiment of the instant invention but operable to measure a single flow or stream is disclosed in U.S. Pat. No. 4,127,028 issued Nov. 28, 1978, to Cox et. al. In this patented structure, a pair of "U" shaped tubes having narrowed base portions and defining but a single flow channel are oscillated out of phase with one another to provide exaggerated distortions as a result of the Coriolis forces produced from flow. Again, whatever the merits or disadvantages of the structure disclosed in the patent, the instant invention could be adapted to such structure.
Another approach to the problem of measuring the small Coriolis forces is described in U.S. Pat. No. 4,109,524, for "Method and Apparatus for Mass Flow Measurement", issued Aug. 29, 1978, to J. Smith.
A particularly advantageous flow meter structure is disclosed in pending U.S. Patent Application Ser. No. 926,468 filed July 20, 1978, by J. Smith, for "Method and Structure for Flow Measurement" now U.S. Pat. No. 4,187,721. In the disclosed device, flow is advantageously determined by oscillating a "U" shaped tube similar to that disclosed in U.S. Pat. No. 4,127,028, and determining flow rates as a function of distortion of the tube around a central axis, or as a function of restoring forces generated to null distortion of the tube. In any event, the invention of the instant application will be described with reference to a Coriolis flow meter substantially as described in the pending patent application.